A case-control study to assess the independent and combined effects of dietary intake, physical activity, body size, reproductive factors, and family history on the risk of colon cancer in whites is proposed. All first primary colon cancer cases (n-2400) and controls (n-2400) from Utah, Minnesota, and participants of the Northern California Kaiser Permanente Medical Care Program will be eligible for the study. Controls will be randomly selected by random-digit dialing and from Health Care Financing Administration records in Utah and Minnesota, and randomly selected from lists of Kaiser Health Plan members in California. Interviews will be conducted by trained interviewers in the study participant's home. Detailed information on dietary intake, physical activity, height, weight, and body fat distribution, reproductive history, and family history of cancer will be ascertained. Analyses will address the hypotheses that: 1) diets high in calories, fat, and protein are associated with an increased risk of colon cancer; 2) diets low in fiber are associated with an increased risk of colon cancer; 3) lower levels of physical activity are associated with an increased risk of colon cancer; 4) nulliparity, late age at first birth and non-use of oral contraceptives are associated with an increased risk of colon cancer; 5) family history of colon cancer is associated with an increased risk of colon cancer; 6) dietary intake and physical activity will be related to risk of colon cancer differently in high and low risk families; 7) physical activity will modify the effect of diets low in fiber and high in calories, fat, or protein on colon cancer risk; 8) dietary intake, physical activity, reproductive events, and family history will have specific effects on different tumor sites within the colon; 9) dietary intake and physical activity will have different effects on risk of colon cancer in males and females. A three-site study is proposed to obtain sufficient numbers of cases and controls to test these hypotheses. This study, while being coordinated in Utah, will be a collaborative effort of investigators from the University of Minnesota and Kaiser Permanente of Northern California. Consistent methods to identify cases rapidly, gather information, and analyze data will be used. Unlike previous studies of dietary intake, physical activity, body size, reproductive factors and colon cancer risk, this study will have sufficient numbers of cases and controls to examine the familial and environmental relationships that exist. Methods have been developed to ensure coordination of study activities.